A research program is proposed to extend the limited knowledge of photochemical degradation reactions of polycyclic aromatic hydrocarbons (PAH) adsorbed on solids. The purpose of the proposed research is to provide more adequate information for the assessment of environmental and occupational health hazards of airborne PAH and reactive intermediates which may be formed during the photodegradation of adsorbed polynuclear aromatic hydrocarbons. A fluidized-bed photochemical reactor will be developed and evaluated for the study of reactions of particulate-adsorbed PAH and PAH epoxides. The stability of some reactive epoxide intermediates which may be formed during the photo-degradation of adsorbed PAH (in aerosols) will be determined under various conditions of light, temperature and humidity. The rate of photo-degradation and chemical half-lives of pyrene, and benzo(a)-pyrene adsorbed on several substrates will be determined under various conditions of light, temperature and humidity. Identification of the products formed during photo-degradation will be sought, with particular emphasis on arene epoxide derivatives.